Its never easy to sustain interest in the race for comptroller -- the official who watches over the citys $60 billion budget and helps oversee $83 billion in public-employee pension funds. But this year, voters need to think about which candidate is willing to face the facts about the long-term spending obligations that endanger New Yorks future.

David Yassky and John Liu, the candidates in Tuesdays Democratic runoff, have some striking similarilities, as was obvious in their final debate last night. Each is a City Council member from an outer borough, Yassky from Brooklyn and Liu from Queens. Both say theyre eager to suggest ways to cut wasteful spending. Both would use the pension funds for some politically pleasing investments, including subsidized housing and job creation, just as Comptroller (and mayoral candidate) Bill Thompson did.

But on the most important issue, theres a big difference.

New York cant continue to make tens of billions of dollars worth of promises for future public-employee pension and health-care payments every year -- at least not without massively hiking taxes or cutting off investment in core public infrastructure.

Yassky has calmly nodded to this reality -- last night, he reminded New Yorkers of “a large public gap.” Hes also thought about how to get the public and other politicians to think about it, too. Liu seems to be in denial.

First, theres pensions. In New York, public employees can retire at 55 (earlier, for uniformed employees) and enjoy generous health-care benefits no longer available in the private sector.

Because of a failure of state and city politicians to acknowledge the obvious -- that this cant continue forever -- well spend $14 billion on benefits this year, dwarfing the money for things like investing in subways and buses.

“Somethings got to give,” Yassky said last night, backing reform. Liu called for new “revenue streams.”

Yassky says that, with such a huge structural budget gap, Albany (which controls pension benefits) should consider legislating less-generous benefits for new public-sector workers. Liu, by contrast, says that new benefits should be negotiated. (Union interests support Lius bid.)

Liu uses his past pension experience as a selling point -- but Yassky has the law on his side here. Under the Taylor Law, pensions are legislative matters, not a matter for negotiation.

The comptroller, through his partial stewardship of city pension funds, can focus attention on the costs of failure to reform.

How? New York, like many public entities, assumes that the pension funds should return 8 percent a year -- ignoring the possibility that taxpayers have to take unacceptable risk to earn such a return.

Yassky has said that hed consider whether such a return is realistic and reasonable -- including in the context of whether New York can afford what it promises to future workers. (Liu did not return a call for comment on this point.)

Yassky has also said that as comptroller, hed help the city “agency by agency” figure out its least productive 10 percent, including whether labor costs are unnecessarily high.

But hed also encourage the city to look at the budget as a whole. That is, hed have us ask: How much are we willing to take away from other parts of the budget to continue paying pension and other unsustainable costs?

Thats important. Liu often talks about how important it is to invest more in mass transit, a worthy goal -- but few people in government admit that spending in one area means that you cant spend somewhere else.

Yassky also says its useful to look creatively across agencies for possible savings, reconsidering how weve done things for decades. For example, he thinks the citys 1990s-era move to two sanitation men on a truck from three may be a good example for other agencies.

And with retirement ages: While some jobs may cause too much wear and tear on a body after 20 years, perhaps people holding certain jobs could do different city jobs throughout their career, possibly working until a later age before being able to collect a city pension.

The comptroller can also offer a useful counterweight to the political notion that in a pickle, the city and state always can hike taxes.

Yassky seems well aware that ill-considered tax hikes can drive jobs out of the city -- that is, that raising taxes can hurt residents who depend on taxpayer money. He said that he thinks the comptroller should consider the long-term costs of tax policy as well as any short-term revenue benefits.

Fixing problems that took years to build will take years, too. But getting the job done requires a reasoned discussion among officeholders about the problems.